This invention relates to a coaxial engine starter for use with automotive engines.
FIG. 1 is a sectional view illustrating a conventional coaxial starter such as that disclosed in Japanese Patent Laid-Open No. 63-192962. As shown in FIG. 1, the coaxial starter includes an armature 1 of a d.c. electric motor, an armature core 2, and a hollow armature rotary shaft 3 having formed inside thereof a wedge-shaped cam surface 3a for providing an over-running clutch function. The armature core is press-fit onto the outer circumference of the armature rotary shaft 3.
Reference numeral 4 designates a commutator of the face type mounted at the rear outer circumference of the rotary shaft 3. The surface against which brushes 5 contact and slide for commutation is defined by a surface perpendicular to the rotary shaft 3. The commutator 4 is connected to an armature coil 6 wound on the core 2.
The brush 5 is urged forward by a spring 5a disposed at its rear side so that the tip of the brush 5 is brought into contact under pressure onto the sliding surface of the commutator 4.
Reference numeral 7 indicates permanent magnets mounted at the inner circumference of the yoke 8 defining a magnetic circuit for generating a magnetic field in the armature 1. The rear end of the yoke 8 is fitted onto the rear bracket 9 and the front end of the yoke 8 is fitted onto the front bracket 10.
Reference numeral 11 indicates a bearing fitted onto the rear end of the rotary shaft 3 and supported by the rear bracket 9. The rear bracket 9 has formed in the outer circumferential flange portion of the recess for accommodating the bearing 11 thereof a plurality of openings corresponding in position and in number to the brushes 5.
Reference numeral 12 designates a plastic brush holder which houses therein the brush 5 and the spring 5a and has stationary contacts 13 for connection to an unillustrated terminal insert-molded at its rear portion, the stationary contacts 13 having secured thereto, by a screw 15, a terminal 14 on which a lead wire 5b of the positive side brush 5 is welded.
Reference numeral 16 designates rollers disposed on the cam 3a formed in the inner surface of the rotary shaft 3, providing an over-running function together with roller springs.
Reference numeral 17 designates a clutch inner member of the over-running clutch mechanism having a bearing 18 mounted on the outer circumference of the middle portion thereof to support the front end of the rotary shaft 3.
Reference numeral 19 indicates a bearing mounted within the front bracket 10 and supports the front end of the clutch inner member 17.
Reference numeral 17a indicates helical splines formed in the inner surface of the clutch inner member 17, the helical splines 17a engaging the helical splines 20c formed in the outer circumference of the middle portion of a pinion shaft 20 having a pinion 20a at its front end and a flange 20b for dust and water resistance.
Reference numeral 21 indicates a stopper mounted on the rear portion of the pinion shaft 20, and 22 indicates a bearing for supporting the rear portion of the pinion shaft 20 mounted in the inner surface of the clutch inner member 17, the bearing 22 supporting the front end of a return spring 23 of the pinion shaft 20.
The pinion shaft 20 is moved forward along the axis while compressing the spring 23 by the stopper 21 until the stopper 21 abuts against the rear end face 17b of the clutch inner member 17 at which the forward movement is completed.
Reference numeral 24 indicates a solenoid switch attached to the rear bracket 9 by bolts 25, the solenoid switch has a function of forwardly moving the pinion shaft 20 and a switching function for turning on the contacts to allow the power supply from the battery to the electric motor upon the closure of the key switch.
Reference numeral 26 indicates a movable assembly for pushing the pinion shaft 20 from the behind it and having a movable contact 28 supported by insulators 27a and 27b.
Reference numeral 26a indicates a plunger, 26b a rod, 26c a second holder, 26d a first holder secured between the plunger 26a and the rod 26b and having mounted thereon the movable contact 28 and the like. The rod 26b is secured to the plunger 26a by caulking its rear end on the rear surface of the plunger 26a.
Reference numeral 29 indicates a spring for urging the pinion shaft 20, the spring 29 being disposed at the outer circumference of the rod 26b between the first holder 26d and the second holder 26c.
Reference numeral 30 indicates a third holder which urges the pinion shaft 20 by a compression spring 31.
Reference numeral 32 indicates a steel ball disposed between the front end of the third holder 30 and a recessed portion of the rear end of the pinion shaft 20 and having a function of supporting a thrust force.
Reference numeral 33 indicates an excitation coil wound on the bobbin 33a of a plastic material for energizing the plunger 26a. Reference numerals 34a and 34b denote a rear core and a front core, respectively, constituting together with a case 35 a magnetic circuit.
Reference numeral 36 indicates a plate of a nonmagnetic material, which is a rear wall of the solenoid switch 24 serving as a stopper for the plunger 26a when it is rearwardly returned.
Reference numeral 37 indicates a packing disposed between the case 35 and the plate 36 and having a water resisting function.
Reference numeral 38 indicates a spring disposed between the plunger 26a and the front core 34b for returning the movable assembly 26 to its home position when the key switch is turned off.
Reference numeral 39 is a through bolt connecting the rear bracket 9 and the front bracket 10.
It will be apparent to those of ordinary skill in the art that the arrangement of the coaxial starter illustrated in FIG. 1 is a sectional view and that the construction details are repeated about the centerline of the starter defined by shaft 3. For example, a plurality of coils comprising armature coil 6 are disposed about the armature 1.
The operation will now be described. First, for the state in which a key switch is off, the excitation coil 33 is not excited because it is in the non-conductive state, and since only the spring force of the spring 38 acts on the plunger 26a, the movable assembly 26 is positioned at the rear portion and the plunger 26a is brought into abutment with the plate 36.
In this state, the stationary contact 13 and the movable contact 28 are in the separated state, so that the electric motor is stopped and the pinion shaft 20 is also located at the rear portion by the spring 23 and stand still with the rear surface of the flange 20b brought into abutment with the front surface of the clutch inner member 17.
When the key switch is turned on, the excitation coil 33 is energized to actuate the plunger 26a, causing the movable assembly 26 to move forward and the movable contact 28 to be brought into contact with the stationary contact 13.
Therefore, the armature coil 6 is energized through the brush 5 and the commutator 4 thereby to start the electric motor.
On the other hand, the pinion shaft 20 is pushed forward by the springs 29, 31 of the movable assembly 26, whereby the pinion 20a is brought into engagement with the ring gear formed around a fly wheel of an engine at the same time the d.c. motor is started.
Immediately after the starting of the engine, the pinion shaft 20 and the clutch inner member 17 are moved together with the ring gear due to the uni-directional over-running function, idling relative to the armature 1.
When the key switch is turned off when the starting has been completed, the electrical power is disconnected, the movable assembly 26 rearwardly returns due to the function of the spring 38 within the solenoid switch 24, and the pinion shaft 20 rearwardly returns by the function of the spring 23.
Since the conventional coaxial starter is constructed as above described, the minimum number of teeth of the pinion is eight, and with such a starter, each coil of the armature coil 6 has generally two turns in order to obtain requisite torque as the d.c. motor, making it difficult to make the outer diameter of the rotary shaft 3 large, so that the assembly of the over-running clutch within the rotary shaft 3 is difficult and disadvantageous in performance because it is necessary to use small-diameter long rollers or a plurality of small-diameter rollers axially arranged in series.